Feat/how to guide/connect domain

[Ashu96]

Short Description

This PR introduces the how-to guide for connecting a custom domain.

Relevant Links

• Connect custom domain

Checklist

• I added page metadata (description, keywords)
• I've added "Can I Use This?" section (if needed, e.g. if documenting a new feature)
• I added What You'll Learn at the top of the page and every item in the list starts with a lower case letter
• I used title case for titles and subtitles (in the main menu and in the page content)
• I checked for typos and grammar mistakes
• I added alt / title attributes for inserted images (if any)